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著者

京都大学大学院薬学Department of Organic Chemistry, Graduate School of Pharmaceutical Sciences, Kyoto University

抄録

The chemistry of metallic samarium (Sm) is of current interest in organic synthesis. Though samarium iodide (SmI<SUB>2</SUB>) is a good synthetic tool (a mild, neutral and ether-soluble one-electron reductant), its sensitivity to air makes it rather difficult to handle. We have been studying the reactivity of Sm to overcome this drawback of SmI<SUB>2</SUB>. Dehalogenation of <I>vic</I>-dihalides with Sm gave alkenes and alkynes. These reductions were accelerated with a catalytic amount of acid. Olefinic double bonds of various α, β-unsaturated carboxylic acid derivatives (ester, amide, nitrile, carboxylic acid) were also reduced to give the corresponding 1, 4-reduction products. Aromatic carbonyl compounds were reduced to the corresponding pinacol coupling products with Sm-I<SUB>2</SUB> or Sm-I<SUB>2</SUB>-Ti (O<SUP>i</SUP>Pr) <SUB>4</SUB> in methanol. <I>Meso</I> isomers were mainly produced in the presence of Ti (O<SUP>i</SUP>Pr)<SUB>4</SUB> Acyl- or alkoxycarbonyl-protected alcohols or amides are deprotected easily and selectively under mild and neutral conditions. Stereoselective allylation and dimerization of optically active imines with Sm and a catalytic amount of I<SUB>2</SUB> have been successfully accomplished. Both Barbier-type allylation and intermolecular pinacol-like coupling reaction of imines were carried out smoothly to give allylation products and <I>C</I><SUB>2</SUB>-2, 2'-ethylenediiminodiethanol derivatives in a highly diastereoselective manner. This novel <I>C</I><SUB>2</SUB>-dimeric amino alcohols bearing primary alcohols catalyzed enantioselective addition of diethylzinc to aldehydes.